This research project bears an integral relationship to the treatment of tumors by photoradiation therapy (PRT). It is proposed that critical gaps in the understanding of the basic processes controlling transmission of visible light for PRT in tissue be filled. The investigation is concerned with the fundamental principles of coherent and incoherent light delivery to, and light transport within, deep-lying normal and tumor tissues, from lasers, arcs, and incandescents for PRT in cancer therapy studies (e.g., as used with the drug hematoporphyrin derivative (HpD)). Aims are: (1) to enhance understanding of the optical processes of scattering, remittance, refraction, diffusion and absorption in tumor, (2) to study the effect of tissue variables (e.g., adiposity), (3) to show how these optical processes and tissue variables may be quantitated and practically utilized for light dosage estimation in medical practice for effective phototherapy, (4) to develop a simple, empirical model for light dosage prediction and to investigate the best methods for the transport of an adequate, uniform light dose to tumor areas. An ancillary objective will be to analyze PRT photon sources and improve existing, or develop (as circumstances permit) such light detection, delivery and methods, as are indicated. Research will involve the physical fields of light and optics of turbid materials. We will concentrate on, but not be limited to, the 600-700 nm region, using incoherent sources and lasers coupled to fiber optics. Experimental designs will study in vitro, mammalian organs, across species followed by human (autopsy) tissue, in vivo animal tissue and tumors, and conclude with non-invasive in vivo measurements on human volunteers. Archival data on interaction of long wavelength visible light with, and transport in, deep-lying tissues (other than skin) are sparse. The long-term objective of this proposed investigation is to compile a needed body of data for the PRT field, which will be clinically applicable to; the generation of therapeutic light, the delivery mode to tumors, tissue transmission spectra, power, and energy deposited at the treatment site, and ultimately, estimation of activating light dose delivered at the tumor targeted for PRT.